What follows is personal opinion.
Back in the day, what you needed to get a job was a high school diploma. Sure, you could find a menial job if you quit school, but a diploma was the key to a good job that could support a family. So many people didn’t finish high school that those who did were the bright stars.
Then, most people got off the farm and more and more people finished high school because that’s what people did. Soon, a diploma was worth much less, because almost everyone had one. How to pick the brightest? Why, you looked for applicants with college degrees! Not so many people had them, so you could pick the brightest out of the bunch that way.
Nowadays, a college degree doesn’t mean as much, but you still need it to even be considered for some jobs. When there are far more job seekers than jobs, employers can pick and choose, and suddenly you need a college degree to do jobs like “night watchman” or “office manager.” It’s not necessary that the degree be in that field sometimes, but a degree shows that you at least can handle college classes, know how to navigate The System, can show up for classes (and thus, your job) regularly enough to not be kicked out, that sort of thing. (Plus, you probably took a bunch of classes that weren’t for your degree, which makes you a supposedly more well-rounded person. College did do that for me.)
Besides, if you have a degree, it still theoretically shows that you’re smarter and better trained than any competitor that doesn’t have one, right? (Deep sarcasm.) That’s why an IT grad with the ink still wet on his degree can get a job in the field and my husband, with no degree (since Reagan changed who can get student loans back in the ‘80s) but with 14 years of experience in the jobs he was interviewing for, can’t.